Cross-language research using synthetic voice-onset-time series over the past 40 years suggests that the Spanish lead contrast is acoustically less salient than the English lag contrast. This study examined monkey identification of a labial consonant-vowel voice-onset-time (CV VOT) series (-60 to +70 ms) in order to obtain a linguistically unbiased estimate of lead versus lag salience. Comparisons were made with both English and Spanish adult human listeners. In a classic two-choice identification test, monkey and Spanish functions were quite variable and showed evidence of sensitivity to three types of voicing cues (lead versus simultaneous versus lag). In contrast, English functions were highly categorical and showed sensitivity to only two types of cues (combined lead/simultaneous versus lag). Next, listeners were explicitly trained via feedback to differentiate stimuli crossing lead and lag boundaries. Here, monkey and Spanish performance was initially more symmetrical than English performance, with the latter showing reduced sensitivity to the lead boundary, but group differences disappeared after extended training. These results provide evidence for perceptual loss in English listeners for aspects of Spanish voicing lead perception.